Synthetic Metals (v.157, #13-15)

Soluble terthiophene-labeled cruciform molecule as a semiconductor for organic field-effect transistor by Kyung Hwan Kim; Zhenguo Chi; Min Ju Cho; Jung-Il Jin; Mi Yeon Cho; Su Jin Kim; Jin-soo Joo; Dong Hoon Choi (497-501).
Cruciform conjugated molecule, 4(HP3T)-benzene bearing terthiophene moieties has been synthesized through Heck coupling reaction using 5-hexyl-5″-vinyl-[2,2′,5′,2″]terthiophene as dendrons and 1,2,4,5-tetrabromo-benzene as the core unit; this molecule has been fully characterized. This terthiophene-based molecule exhibits good solubility in common organic solvents and good self-film forming property. They are intrinsically crystalline as they exhibit well-defined X-ray diffraction patterns from uniform orientations of molecules. Thus, intermolecular interaction can be enhanced to affect the carrier transport phenomena after annealing at 160 °C. The semiconducting property of 4(HP3T)-benzene has been evaluated in organic field-effect transistors. 4(HP3T)-benzene exhibit carrier mobility as high as (3.7 ± 0.5) × 10−4  cm2  V−1  s−1 with an on/off ratio of about 1 × 103.
Keywords: Cruciform molecule; Organic semiconductor; Mobility; Organic field-effect transistor;

Novel donor–acceptor molecules as donors for bulk heterojunction solar cells by Yinhua Zhou; Ping Peng; Liang Han; Wenjing Tian (502-507).
Three novel donor–acceptor molecules (BCPD, BPPD and PDHC) have been investigated as donors for the bulk heterojunction solar cells. BCPD and BPPD have the same acceptor group of TPO while BCPD and PDHC have the similar donor group of carbazole. The absorption data indicates that the introduction of either strong electron-donating group or strong electron-withdrawing group will induce the red shift of ICT transition absorption. Electrochemistry measurement shows that the three compounds present reversible or partly reversible oxidation and reduction processes. When the donor moiety was changed from carbazole to phenothiazine, the oxidation potentials shifted from 1.10 V to 0.72 V. While the acceptor moiety was changed from TPO to CEM, the reduction potentials shifted from −1.42 V to −0.92 V. The bulk heterojunction solar cells using the three compounds as donors and PCBM as acceptor were fabricated. The cell based on PDHC containing strong electron-accepting group shows a relatively high energy conversion efficiency of 0.51% under the illumination of white light at 100 mW cm−2, which is almost two times of the magnitude of the cells based on BCPD and BPPD.
Keywords: D–A molecule; Intramolecular charge transfer; Cyclic voltammetry; Organic solar cell;

New TTF and bis-TTF containing thiophene units: Electrical properties of the resulting salts by Tahar Abbaz; Abdel-K. Gouasmia; Hideki Fujiwara; Takashi Hiraoka; Toyonari Sugimoto; Marc Taillefer; Jean-M. Fabre (508-516).
Series of new TTF and bis-TTF containing a thiophene ring as a substituent or as a spacer group were prepared by using a palladium-catalyzed cross-coupling reaction from tributylstannyl–trimethyltetrathiafulvalene (tMeTTF–SnBu3) and different halogeno and dihalogenothiophene derivatives. The reducing power of each new precursor was determined by cyclic voltammetry. Radical cations salts and charge transfer complexes of the donors with TCNQ were prepared and characterized. The electrical conductivity of these materials was measured and discussed in terms of (electronic) structure.
Keywords: Tetrathiafulvalene; Thiophene; Radical cation; Conductivity; Electrochemistry;

At present work, five new tetrathiafulvalene (TTF) derivatives bearing two or four thiazole groups are prepared, which have been characterized by 1H NMR, IR, MS spectra, elemental analysis and X-ray analysis for 6. The preliminary electrochemical properties of them are investigated by cyclic voltammetry (CV) and two one-electron quasi-reversible waves with redox potentials are observed.
Keywords: Tetrathiafulvalene; Thiazole; Synthesis; Cyclic voltammetry; Crystal structure;

This paper investigates the multi-walled carbon nanotubes (MWNT) and emeraldine formed polyaniline (PANI-EB) composite coating on electro-active paper (EAPap) actuator. EAPap is made with a cellulose paper by coating thin electrodes on both sides of the paper. When an electric field is applied across the electrodes the paper generates a bending displacement. This EAPap material has merits in terms of lightweight, low actuation voltage, low power consumption, dryness, biodegradability and low price. However, the force output and the actuation frequency band are low. Thus, the MWNT with PANI-EB composite is coated on EAPap material to improve its performance as an actuator. This is termed as a hybrid EAPap actuator. The fabrication process of the composite and the actuator performance are explained. In the fabrication process of the composite, the weight percents of MWNT and PANI-EB, and the sonication time have significant effect on the characteristics of the composite as well as the performance of the hybrid EAPap actuator. The weight percents of MWNT and PANI-EB were chosen by considering the electrical property as well as the process capability of the composite. The composites are made with different sonication times, from 2 h to 5 h, and their characteristics are analyzed using FT-IR, TGA, SEM and electrical conductivity measurement. The structural enhancement and electrical conductivity change associated with the sonication time are explained based upon the strong bonding and ionic interaction of MWNT and PANI-EB constituents. Based on the analysis results of the composite, the actuation performance of the hybrid EAPap actuator is evaluated in terms of bending displacement, blocking force, electrical power consumption and efficiency along with sonication time.
Keywords: Electro-active paper (EAPap); Multi-walled carbon nanotubes (MWNT); Polyaniline emeraldine base (PANI-EB); Sonication; Bending displacement; Blocking force;

Carbazole-based aromatic amines having oxetanyl groups as materials for hole transporting layers by S. Lengvinaite; J.V. Grazulevicius; V. Jankauskas; S. Grigalevicius (529-533).
Several oxetane-functionalized aromatic amines have been synthesized by the multi-step synthetic rout. Full characterization of their structure by nuclear magnetic resonance and mass spectroscopy as well as IR spectrometry is presented. The synthesized materials were examined by various techniques including differential scanning calorimetry, thermogravimetry, UV spectrometry, electron photoemission and time of flight techniques. The electron photoemission spectra of the layers showed the ionisation potentials of 5.24–5.67 eV. Time-of-flight hole drift mobility in amorphous layers of bisphenol Z polycarbonate containing 33 wt. % of the electroactive materials ranges from 10−8 to 10−6  cm2/Vs at high electric fields.
Keywords: Aromatic amine; Carbazole; Hole drift mobility; Ionisation potential;

Conductive poly(α,ω-bis(3-pyrrolyl)alkanes)-coated wool fabrics by Richard C. Foitzik; Akif Kaynak; Frederick M. Pfeffer (534-539).
Cross-linked poly(α,ω-bis(3-pyrrolyl)alkanes) were directly applied to woven wool substrates by either chemical, vapour or mist polymerization methods. Choice of dopant could greatly improve the surface resistance. The optimum coating on textiles with the lowest surface resistance, highest colour-fastness and stability was achieved using a mist polymerization method with 1,8-bis(pyrrolyl)octane, iron(III) chloride (FeCl3) as the oxidant and p-toluene sulfonic acid sodium salt (pTSA) as the dopant.
Keywords: Conducting polymers; Cross-linked polymers; Textiles; Conductive textiles;

The Al/tetraamide-I/p-Si Schottky barrier diode (SBD) has been prepared by adding a solution of a novel nonpolymeric organic compound chiral macrocylic tetraamide-I in chloroform on top of a p-Si substrate and then evaporating the solvent. It has been seen that the forward-bias current–voltage (IV) characteristics of Al/tetraamide-I/p-Si SBD with a barrier height value of 0.75 eV and an ideality factor value of 1.77 showed rectifying behaviour. The energy distribution of the interface state density determined from IV characteristics increases exponentially with bias from 5.81 × 1012  cm−2  eV−1 at (0.59-E v) eV to 1.02 × 1013  cm−2  eV−1 at (0.40-E v) eV. It has showed that space charge limited current (SCLC) and trap charge limited current (TCLC) are the dominant transport mechanisms at large forward-bias voltages.
Keywords: Schottky barriers; Schottky diodes; Organic–inorganic semiconductor contact; Tetraamide-I;

Structural properties of carbon prepared from aligned polyacetylene thin films by Mutsumasa Kyotani; Satoshi Matsushita; Takuro Nagai; Yoshio Matsui; Kazuo Akagi (546-550).
Aligned polyacetylene (PA) thin films consisting of fibrils of about 100 nm in diameter were carbonized at 1000 °C in a vacuum or in an argon gas. Structures and morphologies of the carbons prepared from the aligned PA thin films were investigated using Raman spectroscopy, X-ray measurements, and scanning and transmission electron microscopes. The carbonization gave rise to a char of amount of 20% in weight of the PA film. The char was found to contain nanorods of about 10 nm in width. Morphology of the carbon nanorod reflected that of the aligned PA thin film. Subsequently, the char was graphitized by further heating at 2600 °C.
Keywords: Polyacetylene film; Alignment; Fibril morphology; Carbonization; Char; Carbon nanorod;

Heterojunction organic field-effect transistors (OTFTs) based on copper phthalocyanine (CuPc) as p-type and on copper hexadecafluorophthalocyanine (F16CuPc) or 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as n-types were fabricated and studied. They were shown to operate in unipolar mode where hole current was recorded with values approaching those of CuPc-based single-layer device. However, due to a charge transfer phenomenon between CuPc and F16CuPc, the occurrence of a build-in electrical field at the CuPc/F16CuPc interface is shown to influence the transport properties at low drain-source voltages and to induce a non-ideal ohmic behavior in OTFT characteristics. This effect is not observed in the case of CuPc/TCNQ because of a larger energy difference between HOMO and LUMO energy levels of CuPc and TCNQ, respectively.
Keywords: Organic heterojunction; Phthalocyanine; TCNQ; Field-effect transistors;

A blue organic emitting diode derived from new styrylamine type dopant materials by Soon-Ok Jeon; Young-Min Jeon; Joon-Woo Kim; Chil-Won Lee; Myoung-Seon Gong (558-563).
We have designed and synthesized new dopant materials based on the styrylamine moiety, 4-[(1,2-diphenyl)-4′-(N,N-diphenyl-4-vinylbenzenamine)]biphenyl (4) and 4-[(1,2-diphenyl)-4′-(N,N-diphenyl-4-vinylbenzenamine)]terphenyl (8). Blue OLEDs were obtained from new styrylamine dopant materials and compared with those of blue dopant bis[4-(di-p-N,N-diphenylamino)styryl]stilbene (DSA-Ph) and diphenyl[4-(2-terphenyl vinyl)phenyl]amine (R-BD). The ITO/DNTPD/NPB/MADN:dopant/Alq3/Al-LiF device obtained from 4 shows blue EL spectrum at 469 nm and high efficiency 3.02 cd/A at 7 V. 8 also shows blue EL spectrum around λ max  = 468 nm, efficiency of 3.51 cd/A and a current density of 25.94 mA/cm2 (855.7 cd/m2) at 7 V.
Keywords: Blue dopant material; OLED; Styrylamine;

Thin layers of sulfamic acid-doped polyaniline (abbreviated PANI-SFA) were prepared on quartz substrates by chemical polymerization using ammonium peroxydisulfate as an oxidizing agent. A specific feature of PANI-SFA is its reactivity towards nitrite anions, which results in significant changes in the UV–vis-NIR spectra of the PANI-SFA layer accompanied with a decrease of its conductivity. The chemical mechanism of these changes can be described as follows: for low nitrite concentration it involves the removal of the dopant via oxidation of amine nitrogen to N2 whereas for higher nitrite concentration an additional phenomenon such as reduction of polyaniline from its semi-oxidized (emeraldine) state to the fully reduced (leucoemeraldine) one takes place. The observed phenomena enabled us to use PANI-SFA layers as optodes for reagentless determination of nitrite. In buffer (pH 2) solutions of nitrites the relative absorbance of the PANI-SFA layer, at 816 nm, changes linearly with log  C nitrite. For nitrite concentrations exceeding 10−4  M determination based on the dc conductivity measurements is also possible. The optodes can easily be regenerated by treatment with 1 M sulfamic acid.
Keywords: Optical sensor film; Polyaniline; Sulfamic acid; Nitrite determination;

Optical absorption spectroscopy for determining carbon nanotube concentration in solution by Seok Ho Jeong; Ki Kang Kim; Seok Jin Jeong; Kay Hyeok An; Seung Hee Lee; Young Hee Lee (570-574).
A simple method of determining concentration of carbon nanotubes in solution was provided by using optical absorption spectroscopy. The extinction coefficient of single-walled carbon nanotubes in Beer's law was determined after subtraction of the plasmon background. We found that the extinction coefficient was strongly dependent on the wavelength in the resonant region, whereas this was independent of wavelength in the non-resonant region after plasmon subtraction. This work demonstrates that the concentration of unknown carbon nanotubes dispersed in aqueous solution can be easily determined by simply measuring absorbance, once the extinction coefficient of the material is determined in advance.
Keywords: Carbon nanotube; Extinction coefficient; UV/vis spectroscopy;

Core–shell structured and electro-magnetic functionalized polyaniline composites by Xin Li; Jiaoyan Shen; Meixiang Wan; Zhaojia Chen; Yen Wei (575-579).
Core–shell structured and electro-magnetic functionalized polyaniline (PANI) composites were chemically prepared by micro-spherical hydroxyl iron (Fe(OH)) magnet as the hard-template associated with a self-assembly process in the presence of β-naphthalene sulfonic acid (β-NSA) as the dopant. Field emitting scanning electron microscope (SEM) and transmission electron microscope (TEM) measurements indicate that the electro-magnetic functionalized PANI–β-NSA/Fe(OH) composites have a novel core–shell structure, in which micro-spherical Fe(OH) magnet (0.5–5 μm in diameter) is as the core, and self-assembled PANI–β-NSA nanofibers (30–50 nm in diameter) formed on the surface of the Fe(OH) microspheres is as the shell (60 nm in thickness). Moreover, the electro-magnetic properties of the core–shell micro/nanostructured composites are adjustable by changing the ratio of Fe(OH) to aniline monomer.
Keywords: Core–shell structure; Electro-magnetic function; Hydroxyl iron; Polyaniline composite; Self-assembly process;

Electrochromic properties of conducting polymer metal nanoparticles composites by Manoj A.G. Namboothiry; Tylor Zimmerman; Faith M. Coldren; Jiwen Liu; Kyungkon Kim; David. L. Carroll (580-584).
Electrochromic devices were made using a nanocomposite blend of conducting polymer poly(3,4 ethylenedioxythiophene):poly styrene sulfonate (PEDOT:PSS) and metal nanoparticles of silver or gold. Microscopic analysis showed a random distribution of metal nanoparticles with little aggregation in the matrix. The two terminal devices exhibited an increase in absorption that is dependant on the loading of nanoparticles in the polymer. Further, the active electrochromic spectral window showed a bias dependant tuning and a broadened spectral response. All devices exhibited slow relaxivities which we interpret as resulting from the high capacitance of the metal nanoparticles embedded in the polymer matrix.
Keywords: Electrochromism; Nanocomposites; Tenability; Spectral responses;

A facile method was developed for the preparation of core-shell attapulgite@polyaniline (ATP@PANI) composite particles via in situ oxidative polymerization after the surface modification of the attapulgite nano-fibrillar clay (ATP) with anilinium chloride salt. The possible encapsulation mechanism was supposed. The composite particles were characterized by FTIR, UV–vis, and TGA. The core-shell morphologies of the composite particles like Chinese date were confirmed by TEM and SEM. The effect of the concentration of hydrochloric acid on the morphologies and the electrical conductivities of the ATP@PANI composite particles was also investigated.
Keywords: Attapulgite; Polyaniline; Encapsulation; Core-shell; In situ oxidative polymerization; Morphology; Electrical conductivity;

Electrochemical oxidation of glucose on gold–platinum nanocomposite electrodes and platinum-modified gold electrodes was investigated with cyclic voltammetry. Gold–platinum nanoparticles were prepared by reducing aqueous solutions containing chlorauric acid and chloroplatinic acid, and the electrodes were obtained by depositing the gold–platinum nanoparticles from the colloidal solutions onto substrates. The gold–platinum nanocomposite electrodes display high electrocatalytic activity for the glucose oxidation in alkaline solution, showing 0.30–0.35 V negative shift in peak potential as compared with bare gold electrodes, and maintain stable catalytic activity in the reaction. The results of experiments indicate that both gold and platinum act as the dehydrogenation site and gold also functions to regenerate platinum from poisoned platinum. Surface modification of gold electrodes by platinum deposition also increases electrocatalytic activity of the electrodes for the glucose oxidation, showing about 0.10 V negative shift in peak potential, but a gradual decline in reactivity is observed.
Keywords: Gold–platinum nanoparticles; Glucose oxidation; Peak potential; Platinum modification;